Method and device for regulating the coating thickness thickness, especially bond coating thickness, of at least one layer of viscous fluid applied to at least one planar substrate

ABSTRACT

The invention relates to a method and a device for regulating the thickness of coatings or layers, in particular of bond coatings, wherein bonding is controlled in a programmed manner thereby taking into account the influence of disturbance variables. The invention can be used especially in the production of DVDs. The advantages of the present invention are reproducible accuracy in adjusting the thickness of the coating/bond coating and thus an increased production output.

[0001] The invention relates to a method and a device for regulating orcontrolling the coating or layer thickness, especially the bond coatingthickness and can be used in particular in the production of DVDs(digital versatile disks, i.e. versatile writable and readable storagedisks).

[0002] DE-C1-196 05 601 already describes a device for a controlledsurface coating. By means of a nozzle which can be moved parallel to asubstrate surface, a lacquer or varnish is applied uniformly, and by adigitally controllable step motor, the nozzle can be moved to anydesired location during operation, and thus the surface to be coated canbe determined. The influence of the temperature of the substrate to becoated, the temperature of the coating material and its viscosity arenot taken into account during coating.

[0003] DE-A1-38 22 835 discloses a method and a device for lacquering orvarnishing workpiece surfaces. During the operating cycle of a robot, aspraying gun obtains from the robot's control unit a continuously orgradually varying desired value for the lacquer flow. Moreover, thelacquer flow to the spraying gun is measured and readjusted by adjustingthe flow resistance on the flow path between lacquer distributor andspraying gun in accordance with its deviation from the present desiredvalue. Moreover, during one operating circle of the robot, the robot'scontrol unit adjusts continuously or gradually varying values for thesprayer and/or horn air flow of the spraying gun. The method relates tothe application of lacquer by means of a spraying gun and thus differsbasically from the coating method of the present invention in which thecoating material is applied by a dosing pump, a dosing arm being movableover the substrate and a rotary drive for rotating the substrate. Inthis method, especially the quality of the coating of lacquer isimportant. In particular, it is intended to avoid the occurrence ofdrops or blots during the application of lacquer. Therefore, the lacquerflow is adapted to the sprayer air. The problem of regulating thethickness of the coating material is not mentioned in the citedreference.

[0004] It was found that there is a reproducible relation between thetemperature of the substrates to be coated, the temperature of thecoating material and the viscosity of the coating material, on the onehand, and the expected coating thickness during bonding of substrates,on the other hand. FIG. 3 shows, for example, the dependency of theviscosity of the bonding material on the temperature. It was found thatif the substrate temperature changes from 40° to 45° C., the bondcoating thickness changes from 40 to 35 μm. For many fields ofapplication, in particular in the case of DVDs, it is of greatimportance that the bond coating thickness meets narrow tolerances.

[0005] Therefore, it is an object of the present invention to provide amethod and a device for regulating the coating thickness, wherein areproducible high accuracy of the coating thickness is achieved.

[0006] The object is achieved with the features of the claims.

[0007] In achieving the object, the invention starts out from the basicidea of taking into account varying variables (disturbance variables)which influence the coating thickness or bond coating thickness duringcoating, in particular during bonding, and of controlling bonding inaccordance with their influence. During coating/bonding the coatingthickness is measured and deviations from a desired value arereadjusted. The temperature of the substrate(s) and the temperature ofthe bonding material, which influence the viscosity of the bondingmaterial, are taken into account as varying variables. The influences ofthe disturbance variables on the coating thickness and bond coatingthickness are determined empirically, and the aggregates involved in thecoating and bonding process, such as a dosing pump, a dosing arm, arotary drive for the coating material application and bonding materialapplication as well as a connecting means for connecting the substratesand a rotary centrifugal drive are controlled in accordance with analgorithm which takes into account the influences of the disturbancevariables, in order to achieve a coating thickness which meets a givendesired value.

[0008] It is an advantage of the present invention that the coatingthickness can be adjusted very accurately and that there is a very lowreject rate, e.g. in connection with DVDs produced in accordance withthe present invention, so that the production process leads to anincreased yield.

[0009] In the following, the invention is explained in more detail inconnection with the drawings in which

[0010]FIGS. 1a to 1 c are schematic representations of the bondingprocess in which the present invention can be applied,

[0011]FIG. 2 is a block diagram of the program control of the presentinvention, and

[0012]FIG. 3 is a diagram representing the dependency of the viscosityof the bonding material on the temperature.

[0013]FIG. 1a alone can be regarded as a representation of the bondingprocess in general. In this process, a coating/bonding material 7 ispumped by a dosing pump 1 out of a reservoir 6 and sprayed onto asubstrate S1 via a dosing arm 2. The height of the dosing arm 2 can beadjusted with respect to the substrate 1, and said dosing arm can bemoved radially over the substrate. The substrate S1 is located on aplate 9 with is kept in a motion of rotation by a rotary drive 3. Thelayer or coating 8 is thus formed on the substrate S1. Since thetemperature during the coating process and the temperature of thematerial or substrate used during this process are in general notconstant, the coating/bonding material and the substrate(s) havevariable temperatures.

[0014] During bonding of two substrates, a connecting means places thesecond substrate S2 onto the coated substrate S1 (FIG. 1b).

[0015] Moreover, during bonding, excess bonding material of the coating8 between the substrates S1 and S2 is spun off by a rotary centrifugaldrive 5 (FIG. 1c).

[0016] During bonding, the processes according to FIGS. 1b and 1 c alsoinfluence the expected bond coating thickness, e.g. by the connectingpressure and the speed of the rotary centrifugal drive 5.

[0017] It was found that the bonding process as shown e.g. in FIGS. 1ato 1 c is influenced by disturbance variables such as the temperaturesT1 and T2 of the respective partial substrates S1 and S2, thetemperature T3 of the bonding material and the viscosity of the bondingmaterial, so that the bond coating thickness deviates from a givendesired value, which only depends on the bond material flow, itsdistribution on a substrate and the rotational speed of the substrate.

[0018] In accordance with the present invention, reproducible relationsbetween the temperature, the viscosity of the coating material and thebond coating thickness are determined empirically and represented in theform of value tables and curve functions (cf. FIG. 3). The determinedfunctional relations are made the basis of a control program for theaggregates of the coating process.

[0019]FIG. 2 shows a block diagram for controlling the bondingaggregates.

[0020] A computer PC having a memory-programmable controller (SPS) isprovided. The disturbance variables such as temperatures T1 and T2 ofthe respective partial substrates S1 and S2 and the temperature T3 ofthe bonding material 7 and the kind or type B of the bonding materialare inputted into said programmable controller. The PC presets thedesired value. Depending on an adapted software, the outputs 1, 2, 3, 4,and 5 of the programmable controller trigger the corresponding bondingaggregates: dosing pump 1, dosing arm 2, rotary drive 3 for the bondingmaterial coating, connecting means 4 and rotary centrifugal drive 5. Forexample by increasing or decreasing the bond material input, therotational speeds and/or the rotational time and the connectingpressure, the corresponding bonding aggregates then react against orcompensate a deviation of the bond coating thickness from the desiredvalue caused by the temperature change.

[0021] A device according to the present invention for performing amethod for regulating the bond coating thickness comprises preferablysensors for measuring the disturbance variables, a means for controllingthe bond coating thickness during the process and a processor comprisinga PC and a programmable controller for controlling bonding in accordancewith the disturbance variables and the measured bond coatingthicknesses. The sensor for measuring the bond coating thickness ispreferably an optical sensor.

[0022] Preferably, a plurality of sensors for measuring the coatingthickness are provided at different radial distances from the rotationalaxis of the rotary drive 3, so that the coating thickness can bemeasured at different points and can be supplied to the controllerPC/SPS.

[0023] When the method and the device according to the present inventionare used in the production of optical storage disks (DVDs), a desiredvalue for the bond coating thickness of e.g. 55 μm is adjusted, whichhas a tolerance of ±10 μm in the radial direction and a tolerance of ±4μm in the tangential direction.

[0024] In addition to regulating the bond coating thickness, the methodand device according to the present invention can also be used forprecisely regulating the thickness of other viscous coatings onsurfaces, e.g. coatings of lacquer.

1. A method for applying thin coatings or layers of a viscous fluid ontoplane substrates, in particular for forming bond layers between partialsubstrates (S1, S2) or coatings of lacquer on substrates thereby using adosing pump (1) for the coating material (7), a dosing arm (2) which ismovable over the substrate (S1), and a rotary drive (3) for rotating thesubstrate (S1) and by regulating the layer thickness to a desired value,wherein a regulator means controls the controlled variables for thedosing pump, the dosing arm and/or the rotary drive thereby taking intoaccount the influence of varying variables (disturbance variables). 2.The method according to claim 1 , characterized in that the disturbancevariables which are taken into account are the temperatures (T1, T2) ofthe respective substrates (S1, S2) and the temperature (T3) of thecoating material (7).
 3. The method according to claim 1 or 2 ,characterized in that the influence of the disturbance variables isdetermined empirically.
 4. The method according to claims 1 to 3 ,wherein a connecting means (4) for connecting the substrates (S1, S2)after the formation of bond layers and a rotary centrifugal drive (5)for spinning off excess bonding material between the substrates (S1 andS2) after connection are controlled as further controlled variables. 5.The method according to claims 1 to 4 , characterized in that thecoating/bonding is controlled by a PC/SPS (personal computer withprogrammable system) program.
 6. The method according to claim 5 ,characterized in that the dosing pump (1), the dosing arm (2), therotary drive (3), the connecting means (4) are operated by step motorsand that the rotary centrifugal drive (5) is a servomotor.
 7. The methodaccording to any one of claims 1 to 6 , characterized in that thethickness of the coating/bond coating is measured during the process ina non-contacting manner and that deviations from the desired value arereadjusted automatically.
 8. The method according to claim 7 ,characterized in that the desired value is a predetermined coatingthickness range in the radial and tangential directions of thesubstrate.
 9. The method according to claim 7 or 8 , characterized inthat the sensor is an optical sensor.
 10. The use of the methodaccording to any one of claims 1 to 9 in the production of opticalstorage disks.
 11. The use according to claim 10 , characterized in thatat a desired value of the bond layer thickness of 55 μm, the deviationor tolerance of the bond layer thickness is ±10 μm in the radialdirection and ±4 μm in the tangential direction.
 12. A device forcarrying out the method according to any one of claims 1 to 9 comprising(a) sensors for measuring disturbance variables during coating/bondingof substrates, (b) a means for measuring the thickness of thecoating/bond coating during the process, and (c) a processor forcontrolling coating/bonding in accordance with the disturbance variablesand the measured thickness of the coating/bond coating by means of acontrollable dosing pump (1), a dosing arm (2) and/or by means of arotary drive (3, 5).